TrackList has back-pointer to project...

... and Track::GetOwner() is publicized, so that now you can find the
the AudacityProject, if any, that owns a given Track; this will help eliminate
some uses of GetActiveProject

src/Clipboard.cpp

@@ -12,7 +12,7 @@
 wxDEFINE_EVENT( EVT_CLIPBOARD_CHANGE, wxCommandEvent);
 
 Clipboard::Clipboard()
-: mTracks { TrackList::Create() }
+: mTracks { TrackList::Create( nullptr ) }
 {
 }
 

src/ProjectAudioManager.cpp

@@ -767,7 +767,7 @@ void ProjectAudioManager::SetupCutPreviewTracks(double WXUNUSED(playStart), doub
    {
       auto trackRange = TrackList::Get( *p ).Selected< const PlayableTrack >();
       if( !trackRange.empty() ) {
-         auto cutPreviewTracks = TrackList::Create();
+         auto cutPreviewTracks = TrackList::Create( nullptr );
          for (const auto track1 : trackRange) {
             // Duplicate and change tracks
             // Clear has a very small chance of throwing

src/ProjectFileManager.cpp

@@ -204,7 +204,7 @@ auto ProjectFileManager::ReadProjectFile( const FilePath &fileName )
       // the version saved on disk will be preserved until the
       // user selects Save().
 
-      mLastSavedTracks = TrackList::Create();
+      mLastSavedTracks = TrackList::Create( nullptr );
 
       auto &tracks = TrackList::Get( project );
       for (auto t : tracks.Any()) {
@@ -589,7 +589,7 @@ bool ProjectFileManager::DoSave (const bool fromSaveAs,
 
       if (mLastSavedTracks)
          mLastSavedTracks->Clear();
-      mLastSavedTracks = TrackList::Create();
+      mLastSavedTracks = TrackList::Create( nullptr );
 
       auto &tracks = TrackList::Get( proj );
       for ( auto t : tracks.Any() ) {
@@ -643,7 +643,7 @@ bool ProjectFileManager::SaveCopyWaveTracks(const FilePath & strProjectPathName,
       // Copy the tracks because we're going to do some state changes before exporting.
       unsigned int numWaveTracks = 0;
 
-   auto ppSavedTrackList = TrackList::Create();
+   auto ppSavedTrackList = TrackList::Create( nullptr );
    auto &pSavedTrackList = *ppSavedTrackList;
 
    auto trackRange = tracks.Any< WaveTrack >();

src/Track.cpp

@@ -492,7 +492,7 @@ wxDEFINE_EVENT(EVT_TRACKLIST_DELETION, TrackListEvent);
 long TrackList::sCounter = -1;
 
 static const AudacityProject::AttachedObjects::RegisteredFactory key{
-   [](AudacityProject&) { return TrackList::Create(); }
+   [](AudacityProject &project) { return TrackList::Create( &project ); }
 };
 
 TrackList &TrackList::Get( AudacityProject &project )
@@ -505,17 +505,19 @@ const TrackList &TrackList::Get( const AudacityProject &project )
    return Get( const_cast< AudacityProject & >( project ) );
 }
 
-TrackList::TrackList()
+TrackList::TrackList( AudacityProject *pOwner )
 :  wxEvtHandler()
+, mOwner{ pOwner }
 {
 }
 
 // Factory function
-std::shared_ptr<TrackList> TrackList::Create()
+std::shared_ptr<TrackList> TrackList::Create( AudacityProject *pOwner )
 {
-   return std::make_shared<TrackList>();
+   return std::make_shared<TrackList>( pOwner );
 }
 
+#if 0
 TrackList &TrackList::operator= (TrackList &&that)
 {
    if (this != &that) {
@@ -524,6 +526,7 @@ TrackList &TrackList::operator= (TrackList &&that)
    }
    return *this;
 }
+#endif
 
 void TrackList::Swap(TrackList &that)
 {

src/Track.h

@@ -285,9 +285,9 @@ public:
 
    bool HasOwner() const { return static_cast<bool>(GetOwner());}
 
-private:
    std::shared_ptr<TrackList> GetOwner() const { return mList.lock(); }
 
+private:
    Track *GetLink() const;
    bool GetLinked  () const { return mLinked; }
 
@@ -1141,9 +1141,9 @@ class TrackList final
    TrackList(const TrackList &that) = delete;
    TrackList &operator= (const TrackList&) = delete;
 
-   // Allow move
-   TrackList(TrackList &&that) : TrackList() { Swap(that); }
-   TrackList& operator= (TrackList&&);
+   // No need for move, disallow it
+   TrackList(TrackList &&that) = delete;
+   TrackList& operator= (TrackList&&) = delete;
 
    void clear() = delete;
 
@@ -1153,10 +1153,10 @@ class TrackList final
  
    // Create an empty TrackList
    // Don't call directly -- use Create() instead
-   TrackList();
+   explicit TrackList( AudacityProject *pOwner );
 
    // Create an empty TrackList
-   static std::shared_ptr<TrackList> Create();
+   static std::shared_ptr<TrackList> Create( AudacityProject *pOwner );
 
    // Move is defined in terms of Swap
    void Swap(TrackList &that);
@@ -1164,6 +1164,10 @@ class TrackList final
    // Destructor
    virtual ~TrackList();
 
+   // Find the owning project, which may be null
+   AudacityProject *GetOwner() { return mOwner; }
+   const AudacityProject *GetOwner() const { return mOwner; }
+
    // Iteration
 
    // Hide the inherited begin() and end()
@@ -1561,6 +1565,8 @@ public:
    bool HasPendingTracks() const;
 
 private:
+   AudacityProject *mOwner;
+
    // Need to put pending tracks into a list so that GetLink() works
    ListOfTracks mPendingUpdates;
    // This is in correspondence with mPendingUpdates

src/UndoManager.cpp

@@ -254,7 +254,7 @@ void UndoManager::ModifyState(const TrackList * l,
    stack[current]->state.tracks.reset();
 
    // Duplicate
-   auto tracksCopy = TrackList::Create();
+   auto tracksCopy = TrackList::Create( nullptr );
    for (auto t : *l) {
       if ( t->GetId() == TrackId{} )
          // Don't copy a pending added track
@@ -294,7 +294,7 @@ void UndoManager::PushState(const TrackList * l,
       return;
    }
 
-   auto tracksCopy = TrackList::Create();
+   auto tracksCopy = TrackList::Create( nullptr );
    for (auto t : *l) {
       if ( t->GetId() == TrackId{} )
          // Don't copy a pending added track

src/effects/Effect.cpp

@@ -1983,7 +1983,7 @@ void Effect::CopyInputTracks(bool allSyncLockSelected)
    mIMap.clear();
    mOMap.clear();
 
-   mOutputTracks = TrackList::Create();
+   mOutputTracks = TrackList::Create( nullptr );
 
    auto trackRange = mTracks->Any() +
       [&] (const Track *pTrack) {
@@ -2271,7 +2271,9 @@ void Effect::Preview(bool dryOnly)
    } );
 
    // Build NEW tracklist from rendering tracks
-   auto uTracks = TrackList::Create();
+   // Set the same owning project, so FindProject() can see it within Process()
+   const auto pProject = saveTracks->GetOwner();
+   auto uTracks = TrackList::Create( pProject );
    mTracks = uTracks.get();
 
    // Linear Effect preview optimised by pre-mixing to one track.

src/effects/Equalization48x.cpp

@@ -339,7 +339,7 @@ bool EffectEqualization48x::TrackCompare()
    SecondIMap.clear();
    SecondOMap.clear();
    
-   auto pSecondOutputTracks = TrackList::Create();
+   auto pSecondOutputTracks = TrackList::Create( nullptr );
    auto &SecondOutputTracks = *pSecondOutputTracks;
 
    for (auto aTrack :

src/menus/EditMenus.cpp

@@ -256,7 +256,7 @@ void OnCut(const CommandContext &context)
    auto &clipboard = Clipboard::Get();
    clipboard.Clear();
 
-   auto pNewClipboard = TrackList::Create();
+   auto pNewClipboard = TrackList::Create( nullptr );
    auto &newClipboard = *pNewClipboard;
 
    tracks.Selected().Visit(
@@ -361,7 +361,7 @@ void OnCopy(const CommandContext &context)
    auto &clipboard = Clipboard::Get();
    clipboard.Clear();
 
-   auto pNewClipboard = TrackList::Create();
+   auto pNewClipboard = TrackList::Create( nullptr );
    auto &newClipboard = *pNewClipboard;
 
    for (auto n : tracks.Selected()) {
@@ -681,7 +681,7 @@ void OnSplitCut(const CommandContext &context)
    auto &clipboard = Clipboard::Get();
    clipboard.Clear();
 
-   auto pNewClipboard = TrackList::Create();
+   auto pNewClipboard = TrackList::Create( nullptr );
    auto &newClipboard = *pNewClipboard;
 
    Track::Holder dest;

src/menus/LabelMenus.cpp

@@ -190,7 +190,7 @@ void EditClipboardByLabel( AudacityProject &project,
    auto &clipboard = Clipboard::Get();
    clipboard.Clear();
 
-   auto pNewClipboard = TrackList::Create();
+   auto pNewClipboard = TrackList::Create( nullptr );
    auto &newClipboard = *pNewClipboard;
 
    //Apply action on wavetracks starting from